[DevOps]: Simplify site-ingestion launcher configuration

[tomvothecoder]

Description

• Closes [DevOps]: Simplify site-ingestion launcher configuration #333
• Derive standard launcher paths from SIMBOARD_ROOT after loading the site config, and resolve the token-file default from the resulting work directory.
• Move environment and token-file ownership to deployment configuration, remove the unused NERSC launcher config, and update onboarding and cron guidance.
• Reorganize the operational-scripts README with navigation, workflow guidance, tables, and checklists.

Checklist

• Code follows project style guidelines
• Self-reviewed code
• No new warnings
• Tests added or updated (if needed)
• All tests pass (locally and CI/CD)
• Documentation/comments updated (if needed)
• Breaking change noted (if applicable)

Deployment Notes (if any)

• Existing externally managed site configs must not expand SIMBOARD_WORKDIR while sourced; the launcher now derives it afterward.
• NERSC Spin continues to invoke nersc_archive_ingestor directly.
• Validation: make backend-test; make pre-commit-run.
• Screenshots: not applicable (launcher and documentation changes only).
• Remaining risk: operators with external legacy site configs must apply the documented upgrade note before deployment.

[tomvothecoder]

@TonyB9000 This PR is ready for review. It addresses #333